This brings me to, Harper's Island. It's an older show, I believe from 2009, but I watched it this year and was hooked just the same. As you can tell it also takes place on an island. It's a little different because the characters are older (not teens) and the reason why they are all on this island is for a wedding. But it all goes downhill from there after people start going missing and bodies begin to show up everywhere. See the resemblance? I watched the entire show in one day. So if you don't have time to spend on a new show to add to the list, don't worry. This show only has 13 episodes and concludes nicely.
I quickly became obsessed with Agatha Christie's concept of a group of friends with a murderer among them. So I watched the show and read Ten back to back. I still need to read the original but if you're as obsessed with mystery as I am, then I highly recommend both Ten and Harper's Island. (I also watched the Family Guy episode they did on this, "And Then There Were Fewer" LOL) Let me know if you've watched Harper's Island or read Ten. Are there any other shows you would suggest? I love a good mystery.